U.S. Pat. No. 3,842,194 of Jon K. Clemens disclosed a video disc having a playback system utilizing variable capacitance. In one configuration of the Clemens system information representative of recorded picture and sound is encoded in the form of a relief pattern in a relatively fine spiral groove on the surface of a disc record. For example, groove widths about 3.5 micrometers and groove depths of about 1.0 micrometer may be used. During playback a pickup stylus about 2.0 micrometers wide having a thin conductive electrode thereon, for example, about 0.2 micrometer thick, engages the groove as the record is rotated by a supportive turntable. Capacitive variations between the stylus electrode and the record surface are sensed to recover the pre-recorded information.
In the system of the above type the use of a relatively fine record groove and the groove engaging requirements for the pickup stylus results in a stylus tip which is extremely small. In U.S. Pat. No. 4,162,510 to Keizer entitled, "Keel-Tipped Stylus for Video Disc Systems," incorporated herein by reference, a novel keel-tipped pickup stylus structure is disclosed. It has been found, however, that during the playback of a capacitive video disc using this stylus, there is considerable variation in the amplitude of the low frequency signals, especially the audio signals, picked up by the stylus. These variations are accompanied by a hissing sound which is unacceptable for a commercial consumer product.